1. Field of the Invention (Technical Field)
The invention relates to computer assisted edge finishing of machined parts and more particularly to an apparatus and method for learning the path to be machined without preprogramming the path either manually or with software.
2. Background Art
The one area of manufacturing which has stubbornly resisted efforts toward automation and computer assistance is the edge and surface finishing of machined parts. (B.L. Dawson, Automated surface Finishing, Aerospace Engineering, 9(8) pp.25-28, 1989). Although many parts are created through computer-aided design, then produced on computer numerically-controlled (CNC) machines, when they come off the machining line they still require labor-intensive hand finishing.
The 1970s might be classified as the golden years of deburring and surface finishing because of the wealth of innovations and classification of world-wide efforts. During the 1980s work emphasized robotic deburring and finishing. In the 1990s, environmental concerns will play a greater role in manufacturing, and more automation will be introduced to exclude workers from hazardous materials. This must be true of finishing operations as well. (L. K. Gillespie, Deburring and Surface Finishing: The Past Ten Years and Projections for the Next Ten Years, Allied-Signal Aerospace Company, Kansas City Division, KCP-613-4437, Sep. 1990).
Ohtomi (Sadayuki Ohtomi, U.S. Pat. No. 4,894,597, 1990) describes a prior art deburring robot that contains a beam sensor and controller to detect burr positions. The predetermined points to be deburred are manually taught beforehand, either manually or through software, and compared with the data from the sensor and controller, enabling the position taught to be corrected. The grinding tool is mounted on a movable arm which deburrs the mounted workpiece. Ohtomi only describes a deburring device and does not disclose an edge finishing apparatus.
Another prior art deburring device is contained in Dombrowski et al. (David M. Dombrowski et al., U.S. Pat. No. 4,993,896, Feb. 19, 1991). This device uses an industrial manipulator such as an ADEPT ONE to move the deburring tool along the edge of a workpiece. The tool is connected to a pilot which limits horizontal penetration into the edge and exerts pressure to keep the tool in contact with the edge. The device includes a force sensor and linear variable displacement transducer to provide force and position feedback. Like the Ohtomi device, the path for machining must be taught beforehand either manually or by program. Additionally, the machining tool moves around the stationary workpiece.
The quality of the finished edge is directly dependent on the maintenance of a constant contact force. Thus, if control of the tool-workpiece contact force can be improved, quality of the finished edge will improve. This invention provides this control by replacing the force control function of the ADEPT ONE robot with a direct-drive XY table having faster dynamic response. Additionally, this invention improves the speed and efficiency of setup and machining by trajectory learning with guarded moves.